1. Technical Field of the Invention
This invention generally relates to the field of submarine pipelines. In particular, the present invention is directed to an economical heavy concrete weight coating used to keep the submarine pipeline submerged below the surface of the water.
2. Description of the Related Art
Concrete coating is applied on submerged offshore pipelines to provide additional mass to ensure sufficient negative buoyancy. The minimum weight of the coating for this purpose is around 190 pounds per cubic foot (“pcf”). Portland cement with natural aggregates is an inexpensive material that can weight concrete, but it does not meet the 190 pcf criterion. Therefore, heavyweight aggregates, such as iron ore, are used in lieu of natural aggregates. The proportion of iron ore aggregates may be 75% of the total weight of the concrete coating. Consequently, the cost of the coating is high. It is desirable to have a concrete coating that achieves 190 pcf that is less expensive.
Various types of slag are produced during the production of iron and steel. Iron is produced by combining scrap iron or iron ore with a fluxing agent, such as limestone or dolomite, with a fuel, such as coke, in a blast furnace. The result is iron and blast furnace slag. The iron is frequently used as feedstock for a basic oxygen or electric arc furnace to produce steel.
Blast furnace slag is a byproduct of iron production. It is generally non-metallic and includes silicates, aluminosilicates, and calcium-aluminino silicates. The blast furnace slag is often used in concrete or asphalt. The most desirable, and thus common, use of blast furnace slag is in the form of ground granulated blast furnace slag (“GGBFS”). The GGBFS is created by rapidly water-quenching the molten slag to cool and solidify it. The rapid quenching produces a granulated slag that includes sand-sized fragments with little or no crystallization. The granulated slag can be ground (crushed or milled) to very fine cement-sized particles. Hence the name “ground granulated blast furnace slag.” GGBFS has cement-like binding properties, which make it a suitable replacement for or additive to Portland cement.
Air-cooled blast furnace slag is blast furnace slag that is poured into beds or molds and slowly cooled under ambient conditions. During the slow-cooling process, the blast furnace slag forms a crystalline structure. The result is a hardened crystalline slag that can be subsequently crushed or molded. Pelletized blast furnace slag is a variation of air-cooled blast furnace slag. It is formed by cooling and solidifying the blast furnace slag with water and then air quenching it in a spinning drum. The result is pelletized blast furnace slag having a crystalline structure. Air cooled blast furnace slag and pelletized blast furnace slag are sometimes used as a lightweight aggregates in concrete or asphalt. Aggregate is a hard, inert material (such as sand, gravel or slag) that is bound with a cementing material to form concrete.
Steel is made by heating iron in a basic oxygen furnace or electric arc furnace. Oxygen is injected into molten iron in the furnace. The oxygen reacts with impurities such as carbon monoxide, silicon, manganese, and phosphorus to form liquid oxides. The oxygen also reacts with some iron. The liquid oxides combine with lime and dolomite to form steel slag. This steel slag is different than blast furnace slag. Indeed, steel slag does not possess any cementing property as does GGBFS in crushed form.
Steel slag is disposed of as waste, or sometimes used in road construction as aggregate in the granular base (the roadbed below the driving surface), embankments, engineered fill, highway shoulders, and hot mix asphalt pavement.